public class Main {
    public static void main(String[] args) {
        System.out.println("Hello world!");
    }
}
class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 0,right = arr.length-1;
        while (left<right) {
            int mid = left + (right - left + 1) / 2;
            if (arr[mid]>arr[mid-1]) left = mid;
            else right = mid - 1;
        }
        return left;
    }
}